The air intake manifold of an internal combustion engine generally consists of upper and lower intake manifolds, which are attached to each other to form the air intake manifold. The lower intake manifold has “runners” (or conduits), each of which provides fluid communication between the intake manifold and a cylinder of the engine to allow airflow from the intake manifold to the cylinder.
At present, the lower intake manifold is made from aluminum and consists of two parts: a main casting and an insert. The insert is attached to the main casting with screws and sealed against the main casting with a gasket. The runners are part of the insert.
While it is efficient and cost-effective to make the lower intake manifold by injection-molding of a plastic material, a lower intake manifold, which is originally designed to be made from aluminum main casting and insert, can be difficult to make by injection-molding of a plastic material. First, because of the relatively complicated geometry of the lower intake manifold that is originally designed to be made from aluminum main casting and insert, mold cores cannot be removed intact after molding. Thus, only lost-core injection molding can be used to make the lower intake manifold in one piece. However, lost-core injection molding may be prohibitively expensive.
Second, although making the lower intake manifold from two injection-molded parts, such as a main part and an insert that includes the runners, allows removal of mold cores and thus is less expensive, injection-molded parts are often not sufficiently precise to satisfy the required tolerances. Specifically, it is often difficult to keep the distances between runners sufficiently consistent and precise to satisfy the required tolerances, due to, for example, the warping of the injection-molded insert.